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Formulating Equine Diets

The most important component of a horse's diet is forage. However, in some cases, diets need to be supplemented with other feeds, such as concentrates.

Photo: Anne M. Eberhardt

The most important component of a horse’s diet is forage, whether through hay, pasture, or a combination. The equine digestive tract is designed to deal with large amounts of forage; the microbial population is present to deal with the digestion of fiber; and the shape of the intestines (twists and turns) maximizes microbial fermentation, digestion, and absorption of nutrients. While the digestive tract is well suited to a life of grazing, it does not do well when horses are fed little hay or large concentrate (grain) meals. Therefore, it is extremely important that horse owners work toward maximizing the amount of forages in their horse’s diet. If a horse doesn’t consume enough true forage (for example if it has bad teeth and can’t chew hay very well), other high-fiber feeds such as beet pulp may be fed.

A rule of thumb is that a horse should consume at least 1% of its body weight as (dry matter) forage daily. So, a 500 kg horse should consume at least 5 kg (about 12 lbs) of forage each day. Ideally, horses will be offered more than that (closer to 1.5–2.5% of their body weight, depending on the horse). Any concentrate offered (if required) should be fed at 0–1% of the body weight, and should never be fed in amounts exceeding the forage (except in growing horses whose digestive tracts aren’t fully developed or suited for forages). Most horses will consume a total of 1.5–3% of their body weight per day, with the upper amounts being fed to lactating mares or horses in heavy work.

Most horse owners under-appreciate how nutritious forages are for their horses. The 5 kg of hay (even if it were the straight timothy hay described earlier) consumed daily by a 500 kg horse would provide 9.95 Mcal of energy, 485 grams of protein, 24 grams of calcium, and 11.5 grams of phosphorus. The requirements of this same horse (at maintenance) are only 16.65 Mcal of digestible energy, 630 grams of protein, 20 grams of calcium, and 14 grams of phosphorus. If the hay were offered at 2% of the horse’s body weight, its energy, protein, calcium, and phosphorus intake would be in excess.

However, in many cases, hay alone will not provide the required minerals (especially salt and the micro-minerals) for a horse. Offering a trace-mineral salt block would be appropriate for a horse consuming only hay. If you are unsure of the protein content of your hay source, offering a balancer will help “top up” the protein in your horse’s diet. A balancer (or at least a vitamin-mineral supplement) would also be recommended if your hay is a little older and its vitamin content reduced with age.

How does your hay meet your horse’s requirements?

Hay Nutrients

The graph at left depicts how a horse’s protein requirements are met with two different types of hay. For example, a 500 kg mature horse at maintenance easily meets his protein requirements when fed 7.5 kg (1.5% of body weight) of timothy hay. However, if this same horse were fed alfalfa hay, which is much higher in protein because it is a legume (compared to timothy which is a grass), it would be consuming far too much protein. If you recall, excess protein in the diet is metabolized for energy in an inefficient way and excess nitrogen is excreted in urine (this is why you might have an ammonia-smelling barn if you feed alfalfa). If we look at a yearling (weighing only about 320 kg, though it would be 500 kg at maturity), his protein requirements are higher than those of an adult horse.

These protein requirements are not met with timothy hay, but are met with alfalfa. If you were to feed this horse timothy hay, a concentrate would have to be added to make up the protein in the diet, or simply more hay may need to be fed (it would depend on overall energy needs). This is the same situation for pregnant and working horses. In early lactation, a mare’s protein requirements are so high that even alfalfa hay doesn’t have enough protein. This example shows that timothy hay is suitable for most horses, and that by feeding a little more of it, or by introducing some concentrate, protein requirements of most horses are easily met. Further, it shows that alfalfa provides too much protein for most horses.

Concentrate Selection

Concentrates (either cereal grains or commercially available feeds) are usually fed to horses when the horse does not meet its nutrient requirements through forage alone. For example, horses that are lactating or are in heavy work have such high nutrient requirements they physically cannot consume enough hay to meet their needs. Offering concentrates may also be helpful when training a horse or to mix in medicines or supplements. It should be noted that most horses do not need concentrates to meet their major nutritional requirements, as indicated by the previous example with the timothy hay. Most horses are in light to moderate work and can easily get their nutrient requirements through hay.

If your horse’s needs call for a higher-energy (or other nutrient) diet, using commercially available products is a convenient way to provide one with confidence that your horse’s diet is balanced. Some horse owners prefer to mix their horse’s feed, though it should be stressed that advice from a nutritionist be sought. Many horse owners, when designing their own diets, believe that if some is good (especially with respect to vitamins or minerals), more is better. Several minerals and vitamins are toxic to horses at relatively low levels, and it is easy to over-supplement. For example, an owner might feed a commercially available feed (which is formulated to contain the required vitamins and minerals), then feed a vitamin-mineral mix (again, with the some is good, more is better mentality). The owner might also then supplement with specific nutrients (such as a vitamin E-selenium mix). In this example, the horse may be getting three times his requirements of vitamin E and selenium. While vitamin E is relatively non-toxic (though it may affect the absorption of other nutrients), selenium is highly toxic at high levels. Working with a nutritionist is the best way to ensure your horse’s diet is balanced.

Another aspect of selecting the proper concentrate concerns the source of the calories. In terms of energy, calories derived from fat are equal to calories derived from carbohydrates (of course, the amount of calories differs per unit weight, but a calorie is a calorie, regardless of source), though the feeds themselves can be quite different.

For example, when a horse consumes a diet rich in starch and sugar (such as cereal grains), he will digest them into glucose. Some horses are very sensitive to glucose in the blood and will experience “sugar rushes” and will be “hot” after consuming meals such as cereal grains or high molasses feeds. This is very similar to a child’s eating a candy bar and experiencing the sugar rush and associated hyperactivity following its consumption. Owners may actually want this kind of response in their horses, so it should be pointed out that the rush is very short lived (again, think of the crash after a sugar rush). Many people suggest their horses are becoming “hot,” which really refers not to temperature but to temperament. For animals that are especially sensitive to sugar rushes and get “hot” easily, their owners should select feeds that do not contain very high amounts of starch and sugar. The feeding of fat or fiber does not result in significant glucose fluctuations in the blood.

Other problems with sugar and starch types of feed are their potential to cause digestive problems. As indicated above, horses have a limited ability to digest starches, so if high amounts of these types of feeds are fed, more and more will reach the large intestine. Here, the rapid fermentation produces gas, which could result in colic, or acids and toxins, which could result in laminitis. Remember, a healthy digestive tract often results in a healthy horse.

Starch and sugar types of diets also have the potential to negatively affect insulin sensitivity. The hormone insulin regulates blood glucose concentrations, moving glucose from the bloodstream into tissues such as muscle or adipose. If a horse frequently consumes sugar-rich meals, it will have many fluctuations of glucose throughout the day. With the increase in blood glucose comes an increase in blood insulin concentrations that attempt to regulate it. It is believed that frequent peaks in glucose and insulin contribute to insulin resistance. Because of problems associated with insulin resistance, it is becoming popular to see equine diets that are “fat and fiber” types of diets. These diets may have the same amount of energy (calories) per unit weight, but the body metabolizes them differently, and we don’t see peaks in blood glucose and insulin. The feedstuffs in these products include things such as beet pulp, rice bran, and vegetable oil. Because horses may not fare well on feeds high in sugars and starches (in general, especially when fed at high rates), trying to have more of the calories within the diet coming from fiber and fat is probably a good option for most horses.

It should be pointed out that horses on a low-starch and -sugar diet are not on a “low carb” diet (a common misconception). Remember that fiber is a carbohydrate. And, if a horse didn’t consume fiber, it would develop severe digestive upsets and would not be very healthy. So fat and fiber type diets are not low carb, but they are low starch and sugar.

Feed Quality

Many horse owners confuse the concept of quality in relation to their horses’ feed. Most horses do not need high nutritive content hay (such as alfalfa) and do quite well on lower “quality” hay. However, what hay (or grain or supplement) is fed should be of the highest value. Good-quality hay should be green and leafy and should smell good and be free of mold, dust, or other foreign objects (such as barbed wire or dead rodents). It is possible to have very high-protein hay (good nutritional quality) that is moldy and dusty and should really not be fed to horses, while at the same time you might have a low-protein grass hay (lower nutritional quality) that is fresh and green and palatable — and perfectly suited to most horses.

Grains also should be of the highest grade possible, and more and more feed companies are looking to include human-grade products in their feeds. Horses should not be fed general livestock feed, especially feed designed for cattle, as compounds such as monensin are very toxic to horses.

Other Feeding Considerations

Any introduction of new hay or grain should be completed over at least a week, and ideally closer to 10 days. This gives the digestive tract and the microbial population a chance to adapt to the new feed. A good rule of thumb is that on days 1 to 3 of the new feed, the horse is fed 75% of the old feed and 25% of the new. On days 4 to 6, the horse is fed 50% of the old feed and 50% new; on days 7 to 10 it gets 25% old feed and 75% new. Then, by day 11 the horse should be entirely on the new feed. If you have a horse that has colicked before due to a sudden change in diet, this process could be spread out even more, with increments of 10 or 15%, instead of 25%.

As you may have noticed, most of the aforementioned feeding recommendations refer to weight of feeds (kilograms or pounds, where 1 kg = 2.2 lbs). To a nutritionist, weighing feed is critical for two main reasons. First, every “scoop” is different. If a horse owner says they feed “one scoop of oats,” we don’t know if this is one of the big metal scoops, a small coffee can, or some other sized object.

Second, feeds have different densities, and therefore weigh different amounts. For example, 1 gallon (or other volumetric measuring device) of oats weighs significantly LESS than 1 gallon of corn. To add to this, the nutrients within each of those “gallons” are substantially different (because corn and oats have different nutrient profiles). Feed doesn’t need to be weighed every day; once you know how much your scoop weighs, you can just feed by the scoop. Hay flakes can also be weighed to get an idea for how much hay is being offered. While each flake within a bale will differ, if you weigh a few flakes from a few different bales you can determine the average weight of one flake.

Calculating Dietary Intake

Doing any kind of simple ration balancing requires some math—or at least the use of software programs like Microsoft Excel. In an effort to determine what is in your horse’s diet, you need to weigh all components of the diet, find out the nutrient composition of those feed components, and then compare them to your horse’s requirements. Sound complicated? It isn’t too bad!

Example Diet

For example, a 600 kg (where 1 kg = 2.2 lbs, so 1,320 lbs) horse at maintenance gets 8 kg of timothy hay and 2 kg of a commercial feed (with 3.4 Mcal/kg, 12% protein, 0.6% calcium, and 0.4% phosphorus). Simply list the nutrients of interest provided by the different feeds and add them up. Then compare to the horse’s nutrient requirements.

Therefore, this horse is consuming more energy than his requirements and is likely gaining weight. While protein, calcium, and phosphorus are also above requirements (though the calcium and phosphorus are still in the desired ratio), they are not at a level of toxicity. This example demonstrates that this horse could easily consume only 1.2 kg of the commercial feed, which would bring the energy intake to 20 Mcal and would reduce the protein, calcium, and phosphorus overload. Alternatively, he could increase his hay consumption to 10 kg and very easily meet these nutritional requirements (10 kg of hay would provide 19.9 Mcal, 970 g of protein, 48 g of calcium, and 23 g of phosphorus), with no grain at all (think of the financial savings!). Obviously not all nutrients are accounted for but should be in a detailed dietary analysis. This example also shows how easy it is to overfeed our horses. It is no wonder more and more of our horses are becoming obese.

Calculating the above example is made difficult when a horse is kept at pasture. While pasture consumption rates have been estimated, it is likely that a horse will consume more pasture per hour if it is only turned out on a limited basis, compared to if it is out all day. For example, a horse at pasture for one hour per day may spend that entire hour eating frantically while a horse at pasture for 24 hours may just nibble throughout the day.

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